Voltage regulating transformer for series coupled loads

ABSTRACT

An improved voltage regulating transformer particularly useful in series lighting systems is provided which relies upon progressive saturation of its core to give a substantially constant voltage output over a substantially wide range of primary currents.

Umted States Patent 11 1 1 1 3,904,954 Knudson Sept. 9, 1975 [54] VOLTAGE REGULATING TRANSFORMER 2,973,470 2/1961 Kohn 323/60 FOR SERIES COUPLED LOADS 2,999,973 9/1961 Mcdlar 323/60 3,061,769 10/1962 Smyth 323/60 X Inventor: Clarence Knudson, Inglewood, 3,160,784 12/1964 Strecker 323 60 x Calif. 3,522,517 8/1970 Backman ct al.. 323/60 X 3,611,116 101971 B' 1" '1 323 60 X 73 Assignee: Hughey and Phillips, Burbank, Calif. a A

[22] Filed: 1973 Primary ExuminerA. D. Pellinen [21] Appl. No.: 418,862 Attorney, Agent, or FirmBruce L. Birchard [52] US. Cl. 323/48; 315/277; 315/279; [57] ABSTRACT 315/282; 323/61 [51] Int. Cl. G05F 3/06 An improved voltage regulating transformer particu- [58] Field of Search 315/276, 277, 278, 279, larly useful in series lighting systems is provided which 315/282; 323/48, 60, 61 relies upon progressive saturation of its core to give a substantially constant voltage output over a substan- [56] References Cited tially wide range of primary currents. UNITED STATES PATENTS 2,706,271 4/1955 Fletcher 323/60 x 10 3 Drawmg guns I CONSTANT 20% CURRENT SOURCE 21 f NYY'L T 22 23 VOLTAGE REGULATING TRANSFORMER FOR SERIES COUPLED LOADS BACKGROUND OF THE INVENTION The prior art is replete with saturable core and ferroresonant transformers designed to give a substantially constant voltage out of the secondary circuit for a variable voltage into the primary circuit. However, experience has shown that such transformers of the prior art do not function effectively when applied in series-load systems such as are used in street lighting and airport lighting. In airport lighting systems, for example, it is customary to operate wind cone lamps and taxiway guidance signs at constant intensity, day and night, whereas taxiway, runway edge and threshold marker lamps may be operated at lower intensity at night than during the day. In some systems, where a separate power source is not available for the taxiway guidance and other lamps, the constant intensity lamps and the variable intensity lamps may be series coupled to a common constant-current source. When it is desired that the taxiway, runway edge and threshold marker lamps be dimmed the current is dropped to a lower constant level. This reduction in current would be expected to reduce the intensity of all the lamps because the current transformers which would normally be used to supply the voltages to the lamps have their primaries in series across the constant current source. However, the current transformer according to this invention provides a substantially constant voltage at its output terminals despite a 2.5 to l variation in its primary current. Thus, the power provided to the load across this transformer will vary only slightly and, if the load is some form of lamp, its output intensity will vary only slightly despite wide variations in the intensity of the light output from series-coupled lamps not supplied power from a transformer according to this invention; e.g. runway end-identifier lights (REILS) and runway alignment indicator lights (RAILS).

In the constant voltage transformer system according to the present invention a uniquely designed ferroresonant transformer is provided which presents a decreasing primary input impedance with increasing primary current, thus providing a substantially constant output voltage to a secondary load. A conventional ferroresonant transformer presents an increasing input impedance with increasing primary voltage, a characteristic which is totally unacceptable in a series coupled load circuit, such as an airport lighting circuit, for which the present invention is peculiarly adapted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a constant current series connected lighting circuit to which the present invention is applicable;

FIG. 2 is a schematic diagram of a constant current to constant voltage system utilizing a transformer following the teaching of the present invention; and,

FIG. 3 is a plan view of one lamination from the core of the transformer shown schematically in FIG. 2.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT In FIG. 1, a potential E. frequently 440 V.A.C., is applied to terminals 10, ll of controller 12, which, as shown, may be a power transformer with a tapped secondary permitting stepped adjustment of the voltage applied to current regulator 13. Current regulator 13 may be any one of several well known types and does not constitute part of this invention. The constant current level out of regulator 13 is related to the setting of the secondary tap on control 12.

Lamp loads 14, 15, 16 and 17 are shown in FIG. I as I coupled through conventional current transformers l8, I9, 20 and 21, respectively, to the constant current source 13. With the circuit of FIG. 1, adjustment of controller 12 will cause a change in the current output from current regulator 13 and the voltage applied to all of the lamp loads 14 through 17 will be varied simultaneously, as will the light intensity from each of the lamp loads.

Assuming that lamp load 17 is a taxiway guidance light the intensity of which should not vary when the other lamps (which may be marker lights) have their output intensities reduced, as at night, the conventional current transformer 21 should be disconnected from terminals 22 and 23 and the transformer of FIG. 2 substituted therefor. An appropriate change in the lamp type should also be made to fit the secondary voltage characteristics of the substituted transformer.

In FIG. 2 transformer 200 has primary terminals 201 and 202 adapted for connection between terminals 22 and 23, respectively, of FIG. I.

The primary of transformer 200 is split into two sections 203 and 204 which are separated by magnetic shunt 205. The secondary of transformer 200 is split into two sections 206 and 207 separated by magnetic shunt 208. The two secondary windings 206 and 207 are wound on respective insulating bobbins carried by sections 209 and 210 of cruciform core 211 of transformer 200. The material of cruciform (cross-shaped) core 211 exhibits the so-called square loop" magnetic characteristics well known in saturablc core reactors and ferroresonant transformers.

Primary 203 is wound over and suitably insulated from secondary 206. Primary 204 is wound over and suitably insulated from secondary 207.

In FIG. 3 the mechanical configuration of one lamination from the stack of laminations making up the core of transformer 200 is shown for clarity of the meaning ofcruciform core." Little explanation of this FIG. 3 is required except to note that section 300 is removable for the winding of primaries and secondaries thereon and outer perimeter 301 forms a magnetic flux return path for all of the windings. Shunts 205 and 208 are spaced at their ends .030 inches from perimeter 301.

Returning to the transformer and circuit of FIG. 2, conventional ferroresonant transformers have their complete primaries in one location, as at section 203 of FIG. 2. Further in such prior art transformers the two secondary windings, such as 206 and 207 are interconnected out of phase. Additionally, prior art ferroresonant transformers operate their unitary primaries at a flux density below the point of core saturation.

In contrast to the prior art, transformer 200 has two primary sections 203 and 204 the flux from each of which is partially diverted from the other by magnetic shunt 205. Further, secondaries 206 and 207 are connected in phase. Additionally, the primary of transformer 200 goes into saturation within the normal operating range of the transformer in such a fashion that the input impedance to the primary drops with rising primary current, according to a predetermined pattern.

ldeally the input impedance to terminals 20] and 202 of transformer 200 would decrease linearly with an increase in primary current. This relationship has been approximated in the present invention by proportioning primary sections 203 and 204. For example, in one working sample of a transformer according to the present invention primary section 203 had 45 turns and pri- -mary section 204 had 90. turns. As a result of the unique design of transformer 200 magnetizing current flowing through primary section 204 (and, of course,

through primary section 203) and the capacitive or leading current flowing in secondary section 207, core section 210 will saturate at a primary current somewhat value at the point of saturation of primary section 204.

Core section 209 is operated, at least at initial primary current values, below saturation. As the primary current increases core section 210 goes into further saturation and, ultimately at some point above the lowest predetermined operating primary current, core section 209 goes into saturation. As a result of this progressive core saturation there is a progressive decrease in primary impedance and the voltage across the total primary remains nearly constant. As a result the voltage applied to the load remains correspondingly nearly constant, as is desired.

In the previously described working model of the subject invention where primary section 204 had twice as many turns as primary section 203 the voltage across the total primary varied about four percent for a primary current change from 2.8 to 6.6 amperes,

Looking at the secondary side of transformer 200, sections 206 and 207 are connected so that their voltages will be additive. Further, output voltage is derived from all of secondary section 206 and part of secondary 207. Condenser 212 in conjunction with secondary section 207 provides sufficient capacitive ampere-turns (despite the inductive current produced by inductor 213) to maintain core section 210 in saturation at normal load even though the primary current in transformer 200 is at its lowest operating level.

It is well known that transformer core saturation produces distorted and undesirable waveforms which, in a series coupled circuit such as is shown in FIG. 1 causes distorted primary voltages.

This undesirable distortion is reduced significantly by the inclusion of inductor 213 in series with capacitor 212. The combination is tuned to a resonant frequency in the region of third harmonic of the power frequency, (usually just above the third harmonic) and serves to reduce the harmonic content of the flux in core section 210 and to improve the output waveform from transformer 200. In fact, the composite output derived from section 206 and a portion of section 207 yields load currents and voltages approximating those obtained with a sine wave power source.

The output voltage variation for the working model which has been previously mentioned was about five percent over an input current range of 2.8 to 6.6 amperes. ln that model the voltage'obtained from secondary section 206 was about 40 percent of the total output voltage. This percentage may be varied to suit such factors as current operating range, type of load, voltage regulation and waveform.

While a specific embodiment has been described, modifications may be made within the scope of the invention. The following claims are intended to cover such embodiments.

' What is claimed is:

l. A transformer circuit including:

a primary winding adapted for the passage therethrough of a range of primary currents; a secondary winding; and a core having a central cross-shaped portion of material exhibiting square-loop magnetic characteristics, said cross-shaped portion having first, second and cross-arm sections, said core including, in addition, a perimeter member of material exhibiting low magnetic reluctance and having upper, lower and side sections, said upper and lower sections of said perimeter abutting said first and second sections of said cross-shaped portion, respectively;

said primary winding having first and second sections wound on said first and second sections, respectively, of said core;

said secondary winding having first and second sections wound about said first and second sections, respectively, of said core; a condenser coupled across at least a portion of said first section of said secondary winding to produce a flow of leading current therein;

said first portion of said primary and secondary windings, respectively, being wound with sufficient numbers of turns to produce saturation of said first section of said core throughout said range of primary currents; Y 7

said second section of said primary being wound with a number of turns sufficient to produce saturation of said second section of said core at primary currents of a predetermined magnitude within said range but above the lower end thereof.

2. Apparatus according to claim 1 in which said cross-arm section has ends spaced from said side sections of said perimeter member to form a pair of air gaps.

3. Apparatus according to claim 1 in which said first and second primary sections are wound over said first and second secondary sections, respectively.

4. Apparatus according to claim 1 in which the number of turns in said first section of said primary winding is in the order of twice the number of turns in said second section of said primary.

5. Apparatus according to claim 1 in which said first and second sections of said secondary winding are connected in aiding fashion.

6. Apparatus according to claim 1 in which the material of said perimeter member is the same as the material of said central portion.

7. Apparatus according to claim 1 in which said first section of said secondary winding has first and second ends and said apparatus includes, in addition, means for coupling said secondary winding to a load, said means including a first conductor connected to said first end of said first section of said secondary winding and a second conductor connected to said second secdenser and inductor are series resonant at a frequency in the region of the third harmonic of the frequency of the current passing through said primary winding.

10. Apparatus according to claim 1 in which said primary currents are regulated at preselected levels throughout said range. 

1. A transformer circuit including: a primary winding adapted for the passage therethrough of a range of primary currents; a secondary winding; and a core having a central cross-shaped portion of material exhibiting square-loop magnetic characteristics, said crossshaped portion having first, second and cross-arm sections, said core including, in addition, a perimeter member of material exhibiting low magnetic reluctance and having upper, lower and side sections, saId upper and lower sections of said perimeter abutting said first and second sections of said cross-shaped portion, respectively; said primary winding having first and second sections wound on said first and second sections, respectively, of said core; said secondary winding having first and second sections wound about said first and second sections, respectively, of said core; a condenser coupled across at least a portion of said first section of said secondary winding to produce a flow of leading current therein; said first portion of said primary and secondary windings, respectively, being wound with sufficient numbers of turns to produce saturation of said first section of said core throughout said range of primary currents; said second section of said primary being wound with a number of turns sufficient to produce saturation of said second section of said core at primary currents of a predetermined magnitude within said range but above the lower end thereof.
 2. Apparatus according to claim 1 in which said cross-arm section has ends spaced from said side sections of said perimeter member to form a pair of air gaps.
 3. Apparatus according to claim 1 in which said first and second primary sections are wound over said first and second secondary sections, respectively.
 4. Apparatus according to claim 1 in which the number of turns in said first section of said primary winding is in the order of twice the number of turns in said second section of said primary.
 5. Apparatus according to claim 1 in which said first and second sections of said secondary winding are connected in aiding fashion.
 6. Apparatus according to claim 1 in which the material of said perimeter member is the same as the material of said central portion.
 7. Apparatus according to claim 1 in which said first section of said secondary winding has first and second ends and said apparatus includes, in addition, means for coupling said secondary winding to a load, said means including a first conductor connected to said first end of said first section of said secondary winding and a second conductor connected to said second section of said secondary winding intermediate its first and seconds ends.
 8. Apparatus according to claim 1 in which said condenser is serially connected with an inductor across at least a portion of said first section of said secondary winding.
 9. Apparatus according to claim 8 in which said condenser and inductor are series resonant at a frequency in the region of the third harmonic of the frequency of the current passing through said primary winding.
 10. Apparatus according to claim 1 in which said primary currents are regulated at preselected levels throughout said range. 